Study links insect evolution to ability to detect airborne odors

A study of the University of Illinois (UI) reveals that all insects use specialized odorant receptors that enable them to detect and pursue mates, identify enemies, find food and spread disease.

The findings have been newly published in the journal eLife.

Insects often have hundreds of individual odorant receptors, each of which senses a particular type of chemical. Odorant receptors are distinct from gustatory receptors, which enable almost all animals to detect chemicals in watery environments. When vertebrate and invertebrate creatures began to find new niches on land, some evolved the ability to also detect airborne chemicals.

"Odorant receptors evolved from gustatory receptors," said UI entomology professor Hugh Robertson, who led the research.

The researchers used to hold that odorant receptors were a feature of all insects. But in a recent study, they failed to find odorant-receptor proteins in two groups of flightless insects.

In the new study, the researchers revisited these flightless insects, tiny creatures known as firebrats and jumping bristletails. Instead of looking for the odorant-receptor proteins in these critters, they scoured their genomes and the genomes of other six-legged terrestrial bugs for genes that code for the receptors and for coreceptors.

The researchers found numerous odorant-receptor genes in the wingless firebrat and jumping bristletail, but not in the genomes of six-legged bugs that are not insects.

"Unequivocally, we have a full-blown odorant-receptor family in a wingless insect," Robertson said. "That refutes the claim that the whole system evolved with flight.

"Clearly, odorant receptors evolved long before wings and were not an adaptation to flight," he said. "The evolution of odorant receptors had to be an adaptation to something else, and the most obvious thing is terrestriality."